The present invention relates to color improvement of polymer compounds and products molded from those polymer compounds.
The color problem which is addressed by the present invention becomes particularly noticeable in products molded from particular polymers. For example, styrene-acrylonitrile is referred to as "yellow polystyrene," because it has many of the desirable characteristics of polystyrene, but tends to yellow when it is molded. This coloring problem is aggravated as the polymer resin ages.
Some manufacturers attempt to avoid this problem by using less acrylonitrile in their polymers. For example, one major manufacturer offers a styrene-acrylonitrile with only 23% acrylonitrile rather than the 25% offered by other manufacturers.
Deoxygenation has been demonstrated to improve color in some polymers. Deoxygenation is performed on the monomer stream, on the resin, or both. To deoxygenate the monomer stream, the monomer is sprayed into a vacuum chamber prior to polymerization. To deoxygenate the polymer resin, the resin is placed in a vacuum chamber to remove imbibed oxygen.
These deoxygenation techniques were unsuccessfully employed in an attempt to improve the color of styrene-acrylonitrile molded products. Any color improvement was extremely slight.